1. Field of the Invention
The invention relates to an illuminating device for a surgical microscope, having a light source with the aid of which the observed object can be illuminated through a region of the microscope objective situated outside the optical axis, and having two reflecting elements which can be displaced perpendicular to the optical axis, of which the first deflects a portion of the light into a direction perpendicular to the optical axis, and the second deflects this light into an axially close region.
2. Description of the Related Art
Illuminating devices for surgical microscopes mostly use for the illumination a light path which forms only a small angle, frequently in the range of approximately 6xc2x0, with the observing beam path. This is important, for example, when it is desired to observe deeper lying regions during an operation. If the illumination is not approximately parallel to the observing beam path, the region to be observed would then lie in shadow.
Ophthalmic surgical operations place special demands on the illumination. The angle at which the eye is illuminated relative to the observing beam path of the surgeon is important. Good plasticity (i.e., visual characteristics, among them contrast and depth of field) of the image by the formation of shadows on structures in the interior of the eye is achieved in the case of illumination of the eye at an angle of a few degrees, frequently at about 6xc2x0 to the observing beam path. If, by contrast, the eye is illuminated as coaxially as possible relative to the observing beam path (that is to say, the angle between the observing beam path and illuminating beam path is as small as possible), this leads to the formation of the so-called red reflex. The pupil of the operated eye is lit up in a reddish fashion by the light backscattered from the retina. This type of illumination is very advantageous in cataract operations, because tissue remnants which occur upon removal of the lens and are to be removed without fail to prevent complications can be effectively detected in the backlighting of the red reflex. The generation of the red reflex has become an important aid in modern operating techniques.
In addition to the red-reflex illumination, the simultaneous illumination at about 6xc2x0 is advantageous, because the above mentioned plasticity of the image cannot be achieved at the small angels between the illuminating and observing beam paths required for generating the red reflex. However, a red reflex is not desired in all stages of the operation. An optimum illumination module must therefore offer two illumination settings: in the first position, the OP field is illuminated by a combination of the 6xc2x0 illumination and the more coaxial illumination for the generation of the red reflex. Only illumination at 6xc2x0 is performed in the second position.
It is known to deflect a portion of the axially remote light and to use it for axially close illumination (U.S. Pat. No. 4,779,968). The corresponding deflecting devices are, however, attached below the microscope objective, and this reduces the maneuvering distance below the microscope. Also made use of there in the convergent beam path is a beam splitter which runs through the observing beam path, and this impairs the optical quality of the microscope.
It is known to split the light coming from the illumination, a first mirror, which produces the axially remote light, passing a portion of the light onto a second, axially close mirror for axially close illumination (DE 4028 605 A1). This second mirror can be displace perpendicular to the optical axis of the microscope objective such that it is possible to vary the angle formed by the axially close illuminating light with the optical axis of the microscope objective. However, it is not possible for this arrangement to be entirely excluded from the beam path. Because of the deflection with at least two separate deflecting mirrors, this leads to messy imaging of the precision illuminating slit of a microscope slit lamp. Double images are produced.
In a further previously known illuminating device for a surgical microscope (U.S. Pat. No. 5,760,952), the light incident perpendicular to the optical axis o the microscope objective impinges on two deflecting mirrors by means of which the illuminating angle of the axially remote illumination can be varied, and it is possible to influence the quantity of the light which impinges on a further deflecting mirror for the axially close illumination. The angle of the axially close illumination can, however, not be varied.
In an illuminating device of the type mentioned at the beginning (U.S. Pat. No. 4,783,159, FIG. 5), the two reflecting devices can be displaced jointly into the illuminating beam path and out of the same, such that the illumination with the axially close beam can be switched on and off. If the axially close illumination is to be dispensed with, the reflecting elements must be removed from the beam path. The illumination with the axially close beam is performed, however, always on the optical axis of the objective lens; the illuminating angle cannot be varied.
The object of the invention consists in creating an illuminating device of the type mentioned at the beginning which has a greater variability and with the aid of which the angle of the axially closed illumination can be varied.
In the case of an illuminating device of the type mentioned at the beginning, the solution according to the invention consists in that the reflecting elements can be displaced independently of one another.
By displacing the first reflecting element, it is possible to vary the light quantity which impinges on the second reflecting element. A more or less strong red reflex can be produced thereby. If the first reflecting element is pushed completely out of the beam path of the axially remote illumination, absolutely no axially close light is directed to the object for the red reflex. If the first reflecting element is slowly pushed from outside into the beam path of the axially remote illumination, the red reflex is amplified. At the same time, the axially remote regions of the axially remote illumination are covered, such that the angle between the axially remote light still being shone in and the optical axis of the microscope objective is also reduced. If the red reflex is in the meantime to be dispensed with, the first reflecting element is pushed out of the beam path. If the red reflex is subsequently to be produced again, this is achieved after reintroducing the first reflecting element into the beam path at the same angle for the axially close illumination, since the position of the second reflecting element has not been varied for excluding the red reflex.
Since the second reflecting element can be displaced, the angle for the axially close illumination with respect to the observing beam path can be decreased, and thus the quality of the red reflex can be improved as a function of the setting of the magnification factor of the microscope by zoom or Galilei changer. In the case of higher magnification factors, this reflecting element can be placed by the user close to the observing beam paths or even overlapping therewith (thus producing a more intensive red reflex), without unwanted vignetting becoming detectable. Vignetting can occur if the reflecting element is set in a fashion overlapping with the observing beam path in the case of relatively small magnification. Instances of darkening which are felt as disturbing by many users can occur occasionally in the microscope image perceived by the user. Of course, with acceptance of vignetting it is also possible in the case of low magnifications to displace the second reflecting element so far into the beam paths for an improved red reflex that vignetting becomes visible. The user can make the best choice for the concrete situation.